Spread spectrum communication receiver

ABSTRACT

A spread spectrum communication receiver is disclosed, which is provided with a correlator for correlating a received PN code contained in a received signal with a reference PN code contained in a reference signal generated on the receiver side, the output of which is given to pattern judgment means such as a matched filter, etc., and an operation of the initial synchronization of the two PN codes in the correlator is effected by using a judgment output obtained when the pattern of the output of the correlator is in accordance with a predetermined judgment pattern.

FIELD OF THE INVENTION

This invention relates lo a spread spectrum communication receiver andin particular to the improvement for stabilizing the operation andincreasing the precision of a spread spectrum communication receiver oftype, by which received signals are demodulated to obtain data by usingthe output of a correlator, which correlates a pseudo noise code(hereinbelow abbreviated to PN code) contained in the received signalswith a reference PN code.

BACKGROUND OF THE INVENTION

In the spread spectrum communication, as indicated in FIG. 9(a), the PNcode, which is one of binary codes, is modulated with data and thecarrier, which is modulated with the PN code thus modulated, istransmitted. In the figure, reference numeral 31 represents data; 32 isa modulator: 33 is a PN code generator; 34 is a carrier generator; 35 isa modulator; and 36 is an antenna. On the receiver side, as indicated inFIG. 9(b), the signals are received and correlated with a PN codeserving as the reference. Self correlation waveform (in thisspecification, hereinbelow, called correlation spike waveform) having arelatively large amplitude appearing when the two codes are inaccordance with each other or in the neighborhood thereof is treated torestore the data. In the figure, reference numeral 37 is an antenna; 38is a correlator: 39 is a reference PN code generator; 40 is a datademodulator; and 41 represents data.

There is known a convolver as one of matched filters. A convolver is afunctional element performing convolution integral and it serves as amatched filter performing a correlation operation, if the binary codeserving as the reference (in this specification, hereinbelow, calledreference code) is in the time inverted relation with respect to thereceived code.

There are known SAW convolvers as an example of convolvers. From thepoint of view of the construction there are convolvers, (1) in which anair gap is disposed between a piezo-electric body and a silicon layer,(2) in which a piezo-electric body and a silicon layer are formed in onebody through an oxide layer, (3) which is composed only of a Piezoelectric body, etc. All of these execute multiplication operation byinteraction of the two signals, utilizing nonlinear characteristics andintegrate the result of the interaction in an electrode called gatedisposed in the interaction area.

FIG. 10 shows an example of the construction of the SAW convolver, inwhich reference numerals 42 and 43 are transducers; 44 is apiezo-electric body; 45 is an oxide film; 46 is a silicon substrate; and47 is a gate electrode. The signal s(t) inputted through the transducer42 propagates toward the right in the figure and the signal r(t)inputted through the transducer 43 propagates toward the left. Theinteraction between s(t) and r(t) is produced owing to the non-linearcharacteristics of the piezo-electric body--oxide film --siliconstructure and the integral operation is executed and the result of theinteraction is integrated by the gate electrode 47.

The signal c(t) outputted by the gate electrode 47 can be represented bythe following equation; ##EQU1## where A is a constant; T represents thetime necessary for acoustic wave to pass under the gate electrode (inthis specification, hereinbelow, called in-gate delay time); x thedistance measured in the direction of the propagation of s(t); and v thesound velocity.

In general the PN code has a determined period. In the waveform producedon the transmitter side it is often so constructed that there exists acertain relation between one period of the PN code and the length of onebit in the data. Here, in order to make explanation easier, as anexample, it is supposed that the one period of the PN code and thelength of one bit in the data are equal to each other.

On the other hand the relation between the in-gate delay time and the PNcode can be also suitably selected. That is, the in-gate delay time canbe either shorter than, equal to, or longer than the one period of thePN code. The in-gate delay time means an integral domain in thecorrelation operation. Taking the correlation characteristics of the PNcode into account, it is desirable that the integral domain extendsexactly over one period. Therefore, in this explanation, as an example,it is supposed that the in-gate delay time and the one period of the PNcode are equal to each other.

The relations described above are shown in FIGS. 11(a), 11(b) and 11(c).FIGS. 11(a) and 11(b) represent the arrangement of the data and the PNcode, respectively. In the above example the length of the one data bitand one period of the PN code are identical and both of them are equalto l. FIG. 11(c) is a schematical cross-sectional view of the convolverand the delay time within tho length L of the gate electrode is equal tol. The above description is an example for explaining this invention andthe relations among the length of one data bit, one period of the PNcode and the in-gate delay time can be arbitrarily selected.

For the real communication, since when transmitted signals are receivedis unknown on the receiver side, it waits for the reception of thosignals, while inputting the reference signal to one of the transducers.When a signal is received, it is supplied to the convolver through theother transducer. When the PN codes contained in the received signal andthe reference signal, respectively, are in accordance to each other, thecorrelation spike waveform is obtained through the gate electrode of theconvolver. However it is not known at all at which position they are inaccordance. If the position where the two codes are in accordance werenot correctly set, the data could not be restored correctly. Forexample, in the case where the two codes are in accordance in the formindicated in FIG. 12(a), on tho first half of the received code a databit A takes place and on the second half another data bit B takes place.The figure shows the arrangement of the data bits, the received PN codeand the reference PN code, the region indicated by L representing theinteraction region under the gate electrode. The PN code A representsthe time inverted code of the PN code A.

As explained above, some measures should be taken so that the receivedcode and the reference code are in accordance finally at the positionindicated in FIG. 12(b), wherever they are in accordance at first. Herethe period from the moment, where the signal is received, to the moment,where the codes are in accordance with each other at the positionindicated in FIG. 12(b), is called initial synchronization.

In the case where there exists a difference between the clock frequencyof the received PN code and the clock frequency of the reference code,after the initial synchronization has been effected and the codes havebeen positioned, as indicated in FIG. 12(b), the position where they arein accordance with each other is shifted gradually from the arrangementindicated in FIG. 12(b). This shift can be represented, every time thebeginning of the received PN code and that of the reference PN codeencounter, by; ##EQU2## where f_(r) represents the clock frequency ofthe reference PN code; f_(t) the clock frequency of the received PNcode; and N the number of chips constituting one period of the PN code.

That is, even if the initial synchronization is effected, when the clockfrequencies of the codes are different the position where the two codesare in accordance with each other, is shifted gradually from the correctposition and the demodulation to obtain the data becomes impossible.This means that a completely identical clock frequency should be used onthe transmitter side and the receiver side. For a clock oscillator aquartz oscillator is usually used as the reference. Therefore thismethod has drawbacks that not only it is extremely difficult tofabricate plural quartz crystals having a completely same frequency, butalso circumstances such as temperature, humidity, etc. should becontrolled with an extremely high precision.

In order to remove the drawbacks described above, a method is proposede.g. in Japanese Patent Application No. 59- 77789, by which the initialsynchronization described above is effected by generating a pulse(hereinbelow called correlation pulse) by signal-processing thecorrelation spike described above and by making the patternscorresponding to one period of the two PN codes be in accordance witheach other by initializing (resetting) the reference PN code while usingthe correlation pulse stated above.

SUMMARY OF THE INVENTION

However even by such a method there is a problem that the probabilitythat erroneous operations due to noises, etc. take place is high.

Consequently a first object of this invention is to provide a spreadspectrum communication receiver capable of effecting always a stableinitial synchronization in the correlator without any erroneousoperations due to noises.

In order to achieve the above first object of this invention, a firstspread spectrum communication receiver according to this invention, inwhich desired information is obtained by demodulating received signalsby means of a correlator correlating a received PN code contained in thereceived signals and a reference PN code contained in a reference signalgenerated on the receiver side, is characterized in that the output ofthe correlator is inputted in pattern judgment means and the position,where the two codes are in accordance with each other in the correlator,is set correctly by controlling the phase of the reference PN code byusing the output obtained when the inputted pattern is in accordancewith a predetermined judgment pattern.

In this way a correlation pulse corresponding to the polarity of acorrelation spike outputted by the correlator s generated, which pulseis given to a matched filter serving as the pattern judgment means, andthe initial synchronization of the two codes in the correlator iseffected by using the output of the matched filter obtained when thepattern of the pulse given to the matched filter is in accordance withthe predetermined judgment pattern, e.g. the weight in the matchedfilter.

Secondly, even by the prior art method described previously no attentionis paid to the synchronization of the two codes depending on the amountof delay necessary for the signal processing at the generation of thecorrelation pulse measured from the correlation spike and thereforethere is a problem for effecting a correct initial synchronization.

Consequently a second object of this invention is to provide a spreadspectrum communication receiver capable of effecting always a stableinitial synchronization in the correlator by establishing a method forsetting the amount of delay stated above and the setting position andeffecting a synchronization of the two codes depending on the amount ofdelay thus obtained.

In order to achieve the above second object of this invention, a secondspread spectrum communication receiver according to this inventiondescribed previously is characterized in that it comprises reversiblecounting means, which begins the forward counting with the timing of thefront bit of the reference PN code and is switched to the backwardcounting by the correlation pulse generated from tho correlation spikeoutputted by the correlator and it is so constructed that thesynchronization of the received PN code and the reference PN code in thecorrelator is effected by controlling it so that tho input to thecorrelator is started from tho front bit of the reference PN code, whenthe counting value of the counting means has reached a predeterminedvalue, an offset valve being set, depending on the amount of delay atthe generation of the correlation pulse by signal-processing thecorrelation spike.

Owing to the construction described above, always a stable initialsynchronization is effected, because an offset value corresponding totho amount of delay necessary for the signal processing at thegeneration of the correlation pulse from the correlation spike is set inthe reversible counting means included in the two-code synchronizingmeans in the correlator.

Thirdly, according to the prior art method described previously it isnecessary to correct errors in the phase between the patterns of the twocodes due to the difference between the code clock frequencies of thetwo codes, after the initial synchronization has been effected accordingto the prior art method, i.e. to hold the synchronization, and thisholding of the synchronization is effected by extracting the correlationpulse obtained, every time the two codes are in accordance with eachother in the correlator by using a gate pulse with a desired timing soas to initialize the reference PN code.

However, according to such a prior art method there are problems thatthe probability that erroneous operations take place is high, whennoises, etc. are mixed with the timing of the gate pulse, and that along time is necessary for converging the errors, because the errors inthe phase are reduced to 1/2, every time the two cOdes are in accordancewith each other and the initial synchronization of the reference PN codeis effected. Furthermore there is thus another problem that it is notpossible to effect correctly the data demodulation.

Consequently a third object of this invention is to provide a spreadspectrum communication receiver capable of effecting a stable operationby improving the method for holding the synchronization stated above anda fourth object of this invention is to provide a spread spectrumcommunication receiver capable of effecting correctly the datademodulation.

In order to achieve the above third object of this invention, a thirdspread spectrum communication receiver according to this inventiondescribed previously is characterized in that it comprises means forgenerating sampling signals before and after the correlation pulseoutputted by the correlator in time, means for extracting thecorrelation pulse stated above by these sampling pulses, means forcounting the number of extractions, means for generating a phasecontrolling signal when the difference between these count values hasreached a predetermined Value to effect the phase control of thereference PN code, the output of the correlator being inputted inpattern judging means so that the phase of the reference PN code iscontrolled by the output obtained when the outputted pattern is inaccordance with a predetermined judgment pattern.

The amount and the direction of deviation of the correlation pulse aredetected by counting the extractions of the correlation pulse by meansof the sampling pulses. The phase of the reference PN code iscontrolled, depending on this detected amount and the errors in thephase between the two codes are corrected so as to hold thosynchronization.

In order to achieve the above fourth object of this invention, a fourthspread spectrum communication receiver according to this inventiondescribed previously is characterized in that it comprises means forgenerating sampling signals before and after the correlation pulseoutputted by the correlator in time, means for extracting thecorrelation pulse stated above by these sampling pulses, means forcounting the number of extractions, means for generating a phasecontrolling signal when the difference between these count values hasreached a predetermined value to effect the phase control of thereference PN code, and means for demodulating the received signal toobtain the data by extracting the correlation pulse between the twosampling pulses.

The amount and the direction of deviation of the correlation pulse aredetected by counting the extractions of the correlation pulse by meansof the sampling pulses. The phase of the reference PN code iscontrolled, depending on this detected amount, and the errors in thephase between the two codes are corrected so as to hold thesynchronization, and at the same time the received signal can bedemodulated so as to obtain the data by extracting the correlation pulsebetween the two sampling pulses.

Fourthly, according to the prior art method described above for holdingthe synchronization no method for detecting the start timing ofinformation data contained in the data obtained by the demodulation isestablished, which is a problematical point. Consequently a fifth objectof this invention is to provide a spread spectrum communication receivercapable of detecting easily the start timing of the information datacontained in the data obtained by the demodulation by means of anexternal circuit.

In order to achieve the above fifth object of this invention, a fifthspread spectrum communication receiver according to this invention, inwhich desired information is obtained by demodulating received signalsby means of a correlator correlating a received PN code contained in thereceived signals and a reference PN code contained in a reference signalgenerated on the receiver side, is characterized in that it is soconstructed that the data obtained by the demodulation is inputted in aninformation data start timing judgment means and the output obtainedwhen the pattern thereof is in accordance with a predetermined judgmentpattern is given to an external circuit so as to detect the start timingof the information data.

The start timing judgment means consists of e.g. a matched filter, inwhich the data obtained by the demodulation is inputted, and when thepattern thereof is in accordance with the predetermined judgmentpattern, a pulse is outputted. By using this pulse it is possible toknow easily the start timing of the data information.

Fifthly, according to the prior art method described above for holdingthe synchronization the probability that erroneous operations of thoinitial synchronization due to noises, etc. take place is high andfurther no method for detecting the start timing of the data informationcontained in the data obtained by the demodulation is established, whichwas a problem for practical use.

Consequently a sixth object of this invention is to provide a spreadspectrum communication receiver capable of stabilizing the initialsynchronization operation and making the detection of the start timingof the information data contained in the data obtained by thedemodulation easy and precise.

In order to achieve the above sixth object of this invention, a sixthspread spectrum communication receiver according to this invention, inwhich desired information is obtained by demodulating received signalsby means of a correlator correlating a received PN code contained in thereceived signals and a reference PN code contained in a reference signalgenerated on the receiver side, is characterized in that it is soconstructed that the output of the correlator is inputted in firstpattern judgment means, the initial synchronization of the two codes inthe correlator is effected by the output obtained when the inputtedpattern is in accordance with a pattern, in which all the bits are "1"or "0"; at the same time the data obtained by the demodulation isinputted in second pattern judgment means; and the start timing of thedata information contained in the data obtained by the demodulation isdetected by means of the output obtained when the pattern inputtedtherein is in accordance with a predetermined pattern consisting ofBARKER codes or phase inverted codes thereof.

In this way the position, where the two PN codes are in accordance witheach other in the correlator by controlling the phase of the referencePN code by means of the output of the first pattern judgment means andthe output of the second pattern judgment means is given to an externalcircuit in order to make it detect the start timing of the data obtainedby the demodulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of this invention;

FIG. 2 is a timing chart for explaining the operation of a correlationpulse generator in the embodiment indicated in FIG. 1;

FIG. 3 is a timing chart for explaining the initial synchronizationoperation in the embodiment indicated in FIG. 1;

FIGS. 4, 5 and 6 are block diagrams illustrating an example of theconstruction of a first matched filter in the embodiment indicated inFIG. 1;

FIGS. 7 and 8 are block diagrams illustrating an example of theconstruction of a second matched filter in the embodiment indicated inFIG. 1;

FIG. 9(a) is a block diagram illustrating the construction of a priorart spread spectrum communication transmitter;

FIG. 9(b) is a block diagram illustrating the construction of a priorart spread spectrum communication receiver;

FIG. 10 is a cross-sectional view illustrating the construction of aconvolver;

FIGS. 11(a), 11(b) and 11(c) show the relation among the arrangement ofa data bit, that of a PN code and that of the gate electrode;

FIGS. 12(a) and 12(b) are schemes for explaining that the received PNcode and tho reference PN code should be correctly arranged;

FIG. 13 shows schemes illustrating the structure of transmitted data;

FIGS. 14(a) and 14(b) show waveforms for explaining the setting of anoffset value for an up-down counter used in the embodiment describedabove;

FIGS. 15 and 16 show waveforms for explaining the synchronizationholding operation and the data demodulation operation, respectively, inthe embodiment described above;

FIG. 17(a) indicates self correlation characteristics of a BARKER code;and

FIG. 17(b) indicates self correlation characteristics of a phaseinverted BARKER code.

DETAILED DESCRIPTION

Hereinbelow this invention will be explained, referring to preferredembodiments indicated in the drawings. FIG. 1 is a block diagramindicating the construction of a spread spectrum communication receiver,which is an embodiment of this invention. In which reference numeral 1is a correlator; 2 is a correlation pulse generator; 3 is a firstmatched filter; 4 is an up-down counter; 5 is a reference PN codegenerator; 6 is a sampling pulse and window pulse generator; 7 is adigital phase lock loop circuit; 8 is a PN code phase control pulsegenerating circuit; 9 is a binary data demodulation circuit; and 10 is asecond matched filter.

In FIG. 1, the correlation pulse generator 2 generates a correlationpulse (e) obtained by separating correlation spikes (d) appearing when areceived PN code is in accordance with a reference PN code (h) in thecorrelator 1 or in the neighborhood thereof into positive and negativeones, depending on their polarity. The first matched filter 3 outputs apulse (f) (initial synchronization detection signal), when the patternof the correlation pulse (e) outputted by the correlation pulsegenerator 2 is in accordance with a predetermined judgment pattern.

The up-down counter 4 is initialized by a strobe pulse (i) outputted bythe reference PN code generator 8 and up-counts, starting from an offsetvalue (a) set by an external circuit such as a microprocessor, etc.However, when a pulse (f) is outputted by the first matched filter 3,triggered by the pulse (f), it begins to down-count and generates aborrow pulse (g).

The reference PN code generator 5 outputs the reference PN code (h) andthe strobe pulse (i) indicating the front bit thereof on the basis ofinitial information (c) of the reference PN code set by the externalcircuit.

The sampling pulse and window pulse generator 8 outputs sampling pulses(j), which sample and extract a correlation pulse (e) outputted by thecorrelation pulse generator 2, and a window pulse (k). The digital phaselock loop circuit 7 holds the synchronization between the received PNcode contained in the received signal (b) inputted in the correlator 1and the reference PN code (h) contained in the reference signal.

The PN code phase control pulse generating circuit is triggered bypulses (g) and (l) outputted by the up-down counter 4 and the digitalphase lock loop circuit 7 and outputs a phase control pulse (m) for thereference PN code (h). The binary data demodulation circuit 9demodulates the inputted signal to obtain binary data by the correlationpulse (e) outputted by the correlation pulse generator 2 and the windowpulse (k) outputted by the sampling pulse and window pulse generator 6.The second matched filter 10 outputs (o), when the binary data (n)outputted by the binary data demodulation circuit 9 is in accordancewith the predetermined pattern.

The circuit described above are triggered by respective pulses forstarting the reception operation outputted by the external circuit notshown figure to start respective operations.

Now the operation of tho embodiment of this invention described abovewill be explained more in detail. In order to facilitate theexplanation, it is supposed here as an example that one period of the PNcode and the length of a data bit as well as the integration domain inthe correlator 1 and one period of the PN code are in accordance witheach other.

When a pulse for starting the reception operation is outputted by theexternal circuit, the reference PN code generator 5 gives the correlator1 the reference PN code (h) contained in the reference signal on thebasis of the initial information (c) of the PN code set by tho externalcircuit. When a spread spectrum communication signal is received and thereceived PN code contained in the received signal (b) is in accordancewith the reference PN code (h), a reference spike (d) is outputted fromthe correlator 1 to the correlation pulse generator 2. The correlationpulse generator 2 separates correlation spikes (d) into positive andnegative ones and generates a correlation pulse (e), as indicated inFIG. 2, which pulse is given to the first matched filter 3, the digitalphase look loop circuit 7 and the binary data demodulation circuit 9.

However, as stated previously it is unknown at what position tho two PNcodes are in accordance with each other in the correlator 1 and sincereceived data cannot be demodulated correctly, unless the position wherethe two codes are in accordance with each other is set correctly, theinitial synchronization should be affected so that they are inaccordance finally at the position as indicated in FIG. 12(b). Accordingto this invention this initial synchronization operation is effected asfollows.

Transmitted data consist of preamble data and information data, asindicated in FIG. 13(a). Further the preamble data include an initialsynchronization pattern and an information data start timing detectionpattern, as indicated in FIG. 13(b), and the correlation pulse (e)outputted by the correlation pulse generator 2 is inputted in the firstmatched filter 3. The first matched filter 3 outputs a pulse (f) to theup-down counter 4, when the pattern of the correlation pulse (e) is inaccordance with the set predetermined pattern.

The up-down counter 4 is initialized by the strobe pulse (i) indicatingthe front bit of the reference PN code (h) outputted by the reference PNcode generator 5 and repeats the up-count, starting from the offsetvalue (a) set by the external circuit, until the pulse (f) is outputtedby the first matched filter 3. When the pulse (f) is outputted by thefirst matched filter 3, the up-down counter 4 is switched from theup-count to the down-count with the timing of the pulse and when thecount value of the counter 4 is "0", outputs a borrow pulse (g) to thePN code phase control pulse generating circuit 8.

The PN code phase control pulse generating circuit 8 is triggered by theborrow pulse (g) stated above and outputs a phase control pulse (m) forthe reference PN code (h) to the reference PN code generator 5, thesampling pulse and window pulse generator 6 and the digital phase lockloop circuit 7.

By a series of the operations described above the received PN code andthe reference PN code (h) are set finally so as to be in accordance witheach other.

FIGS. 4, 5 and 6 show an example of the construction of the firstmatched filter 3.

In FIG. 4, reference numeral 11 is a shift register; 12 is a pulsecounter and 13 is a comparator.

The shift register 11 consists of a plurality of shift registers SR₁˜SR₂ connected in series with each other, as indicated in FIG. 5, eachof which is driven by a code clock. There are disposed an outputterminal for every predetermined length and the output of every outputterminal is given to the pulse counter 12.

The pulse counter 12 counts the total number of pulses outputted inparallel by the shift registers and converts the count into binary data,which are outputted to the comparator 13. This pulse counter 12 consistsof e.g. a plurality of half adders 14 and a full adder 15, as indicatedin FIG. 6.

The parallel outputs of a pair of the shift registers are inputted in ahalf adder 14, where a half addition is effected. As the result theinput is converted into binary data by assigning the addition output tothe order of 2⁰ and the carry output to the order of 2¹.

Furthermore the outputs thus converted into binary data are inputted inthe full adder 15, where they are added to each other. In this way thetotal number of the pulses outputted in parallel is converted intobinary data.

The comparator 13 compares the binary data outputted by the pulsecounter 12 with a threshold value set by the external circuit andoutputs a pulse, when the binary data have reached the threshold value.

In the first matched filter 3 constructed as described above, e.g. inthe case where all the elements of the pattern of the transmitted datafor the initial synchronization are "1", a correlation pulse isgenerated even for the case indicated in FIG. 12(a). That is, thepositive side correlation spike is produced in a period, which is 1/2 ofthe period of time T (hereinbelow called delay time) corresponding tothe integral domain of the correlator 1 and no negative side correlationspike is produced. Consequently, while positive side correlation spikesare generated by the correlation pulse generator with the same period asthe correlation spikes, no negative side correlation pulses areproduced.

This correlation pulse is inputted in the shift register 11 and in thisshift register 11 there is disposed an output terminal for every 1/2 ofthe delay time T, as indicated in FIG. 5. Consequently, if the signal isreceived normally, the number of pulses outputted in parallel isincreased by 1 for every 1/2 of the delay time T and is converted intobinary data by the pulse counter 12, as described previously. Afterthat, when the binary data has reached the threshold value, thecomparator 13 outputs a pulse.

According to the construction stated above of the first matched filter3, even if abnormality due to noises, etc, is produced in the output ofthe correlator 1, it is possible to effect matching with only normalcorrelation pulses.

Furthermore the interval of the output terminals set for the pluralityof shift registers SR₁ ˜SR₂ constituting the shift register 11 can bemodified, depending on the pattern of the transmitted data for theinitial synchronization.

FIGS. 7 and 8 show an example of the construction of the second matchedfilter 10. In FIG. 7, reference numeral 21 is a shift register; 22 is apulse counter and 23 is a comparator.

The shift register 21 consists of a plurality of shift registers SR₁'˜SR₂ ' connected in series with each other, as indicated in FIG. 8,Which are driven by a clock, whose period is equal to the length of onedata bit, here is disposed an output terminal for every shift register.

Demodulation data are inputted in the shift register 21 and an inverterINV is connected properly with the output of every shift register sothat pulses are outputted by all the shift registers SR₁ '˜SR₂ ', whenthe demodulation data stated above are in accordance with the patternset for detecting the start timing of the information data contained inthe transmitted preamble data, as indicated in FIG. 13(a). The output ofevery shift register is inputted in the pulse counter 22.

The pulse counter 22 and the comparator 23 are constructed in tho sameway as those described above. The pulse counter 22 counts the totalnumber of the pulses outputted by the shift register 21 and converts itinto binary data, which is inputted in the comparator 23. The comparator23 compares these binary data With a threshold value set by the externalcircuit and outputs a pulse, when the binary data have reached thethreshold value.

Now the method for setting the offset value (a) of the up-down counter 4will be explained. The offset value stated above corresponds to theamount of delay necessary for the signal processing for generating thecorrelation pulse from the correlation spike.

For example, as indicated in FIG. 14(a), the difference in the phasebetween the received PN code and the reference PN code (h) in thecorrelator is represented by T. Then, as indicated in FIG. 13(b), it isafter T/2 measured from the moment of the generation of the strobe pulse(i) indicating the front bit of the reference PN code (h) that the twocodes are in accordance with each other and the correlation spike (d) isgenerated.

Ideally it is desirable that the up-down counter 4 is switched from theup-count to the down-count, when the correlation spike (d) is generated.However, as indicated in FIG. 14(b), since in reality the up-downcounter 4 is switched over from the up-count to the down-count after theamount of delay τ necessary for the signal processing for generating thecorrelation pulse from the correlation spike, no normal initialsynchronization can be effected.

Therefore an offset value t is set in the up-down counter 4 in order toequalize the period of time T_(up), during which the up-count iseffected, to the period of time T_(down), during which the down-count iseffected. This offset value t is given by; ##EQU3##

When the offset value given above is set in the up-down counter 4, it ispossible to effect always a stable initial synchronization.

When the initial synchronization is realized in this way, thearrangement relation between the two codes is as indicated in FIG.12(b).

However, if there is a difference between the code clock frequencies ofthe two codes, the position where the two codes are in accordance witheach other is shifted gradually from the arrangement relation indicatedin FIG. 12(b). That is, even if the initial synchronization has beenonce established, if the code clock frequencies of the two codes aredifferent, the position where the two codes are in accordance with eachother is shifted gradually from the normal position.

For this reason, according to this invention measures described beloware taken in order to hold the synchronization by correcting the shiftdescribe above, i.e. the difference in the phase.

The sampling pulse and window pulse generator 6 and the digital phaselock loop circuit 7 are initialized by the phase control pulse (m) ofthe reference PN code (h) outputted by the PN code phase control pulsegenerating circuit 8.

As indicated in FIG. 15, the circuit 6 stated above generates samplingpulses S₁ and S₂ before and after the correlation pulse (e) obtained atthe correct positional relation in time, as indicated in FIG. 12(b), andoutputs it to the circuit 7. The circuit 7 samples always thecorrelation pulse (e) by using the sampling pulses S₁ and S₂ so as tomonitor the direction of the deviation of the correlation pulse.

The circuit 7 stated above counts samplings by these two sampling pulsesby means of an internal counter, every time a sampling is effected, andwhen there is a difference between the samplings and this difference hasreached a predetermined value, it outputs a pulse (l) indicating theamount of advance or delay to the circuit 8.

The circuit 8 is triggered by the pulse (l) and gives the reference PNcode generator 5 the phase control pulse of the reference PN code (h)corresponding to the amount of the detected deViation of the correlationpulse obtained by using the two sampling pulses so as to control thephase. In this way errors in the phase between the two codes arecorrected and the synchronization can be thus held.

It is possible to effect a demodulation of the inputted signal to obtaincorrect data by means of the binary data demodulation circuit 9, asdescribed below, owing to the fact that the initial synchronization inthe correlator 1 and the hold of the synchronization of the received PNcode and the reference PN code can be effected as explained above.

As indicated in FIG. 16, the positional relation between the correlationpulse (e) and tho sampling pulses S₁, S₂ is always maintained.

The sampling pulse and window pulse generator 6 generates a window pulse(k) having a width, which is equal to the distance from the rising edgeof the sampling pulse S₁ to the falling edge of the sampling pulse S₂,as indicated in FIG. 13, and outputs it to the circuit 9. The circuit 9extracts the correlation pulse (e) by using the window pulse (k) andeffects a correct demodulation to obtain data.

Now, in order to treat the data obtained by the demodulation by means ofthe external circuit, it is necessary to detect the start timing of theinformation data after the establishment of the initial synchronization.

For this purpose a second pattern set for the detection of the starttiming is contained in the transmitted data after the first pattern setfor the initial synchronization. Further the second matched circuit 10is weighted, corresponding to the second pattern stated above.

The data (n) obtained by the demodulation is given to the second matchedcircuit 10 and it is judged whether it is in accordance with the secondpattern or not. When they are in accordance with each other, the secondmatched circuit 10 outputs a pulse (o). The external circuit can detectthe start timing of the data obtained by the demodulation by using thispulse.

In this case it is specifically appropriate to use particular patternsas the first and the second patterns as described below.

That is, (a) as the first pattern a pattern, for which all the bits are"1", and as the second pattern a pattern consisting of phase-invertedBARKER codes are used, or (b) as the first pattern a pattern, for whichall the bits are "0". and as the second pattern a pattern consisting ofBARKER codes (not phase-inverted) are used. At the same time the firstand the second matched circuits 3 and 10 are weighted, corresponding torespective patterns.

When the first particular pattern as indicated in (a) is used, thecorrelation spike is generated, even in the case indicated in FIG.12(a). That is, since the correlation spike appears always with a periodof 1/2 of the delay time corresponding to the integral domain of thecorrelator 1, the speed of tho operation of the initial synchronizationcan be increased.

When the second particular pattern as indicated in (a) is used, owing tothe excellent self correlation characteristics of the BARKER code, asindicated in FIG. 13(b), even if the initial synchronization isterminated early, as stated previously, since all spurious due to thefirst particular pattern at that time appears on the positiVe side, itis easy to separate the detection pulse of the start timing from thisspurious.

In the same way, also when the first particular pattern as indicated in(b) is used, it is possible to increase the speed of the operation ofthe initial synchronization and further when the second particularpattern as indicated in (b) is used, an effect similar to that describedabove can be obtained owing to the self correlation characteristics asindicated in FIG. 14(a).

As explained above, according to the first invention, since the initialsynchronization operation is effected by using the output obtained whentho output of the correlator is in accordance with a predeterminedpattern, no erroneous operations due to noises, etc. take place and astable initial synchronization operation can be always effected.Therefore the effect for practical use is great,

According to the second invention, since the offset value of the up-downcounter contained in the synchronizing moans for the two PN codes in thecorrelator is set so as to correspond to the amount of delay, it ispossible to effect always a stable initial synchronization.

According to the third invention, since the direction of deviation andthe amount of deviation of the correlation pulse after the establishmentof the initial synchronization of the two codes in the correlator arealways monitored and the difference in the phase between the two codesis corrected, the synchronization is surely held.

According to the fourth invention, since the direction of deviation andthe amount of deviation of the correlation pulse after the establishmentof the initial synchronization of the two codes in the correlator arealways monitored and the difference in the phase between the two codesis corrected, correct data are obtained by demodulation owing lo thefact that the synchronization is surely held.

According to the fifth and the sixth inventions, it is possible tostabilize the initial synchronization and to increase the speed thereofby using the particular patterns for detecting the initialsynchronization and the start timing of the demodulated data. Furtherthe initial synchronization is established early and it is possible toseparate easily the start liming detection pulse from spurious due tothe pattern of the data for effecting the initial synchronization.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A spread spectrumcommunication receiver comprising:correlating means for correlating areceived PN code contained in a received signal with a reference PN codecontained in a reference signal; correlation pulse generating means forgenerating a series of correlation pulses, corresponding to the polarityof a correlation spike outputted by said correlating means; referencesignal generating means for generating said reference signal; means forgenerating sampling pulses before and after said correlation pulse intime and extracting a correlation pulse from said series of correlationpulses by using those sampling pulses; digital phase lock means forholding the synchronization between said received PN code and saidreference PN code; phase control means for controlling the phase of saidreference PN code, responding to the output of said digital phase lockmeans; and data demodulation means for demodulating said received signalto obtain data by extracting a correlation pulse from said series ofcorrelation pulses by using a window pulse having a time intervalbetween said sampling pulses generated before and after said correlationpulse in time.
 2. A spread spectrum communication receivercomprising:reference PN code generator means for generating a referencePN code; convolver means for correlating a received PN code contained ina received signal with said reference PN code to generate a correlationspike; correlation pulse generator means for generating a series ofcorrelation pulses corresponding to the polarity of said correlationspike from said convolver means and having a pattern; detecting meansfor detecting coincidence between said pattern of said series ofcorrelation pulses and a predetermined pattern, and for producing adetection signal upon detection of said coincidence; an up/down countersupplied with a start signal indicative of the start of said referencePN code and supplied with said detection signal from said detectingmeans, said counter starting counting in one of up and down directionsin response to receipt of said start signal, changing the countingdirection with respect to an obtained count value in response to receiptof said detection signal, and producing an output pulse when the countvalue reaches a predetermined value; and phase control means responsiveto said output pulse of said counter for producing a control signal forcontrolling the phase of said reference PN code.
 3. The spread spectrumcommunication receiver according to claim 2, wherein said up/downcounter is initialized with an offset count value which is a function ofa delay time from said correlation spike to a point in time at whichsaid detecting means detects said coincidence, and wherein said countingin response to said start signal starts from said offset count value. 4.The spread spectrum communication receiver according to claim 2, whereinsaid code generator means includes means for generating said startsignal, and includes means responsive to said control signal from saidphase control means for controlling the phase of said reference PN code.5. A spread spectrum communication receiver comprising:reference PN codegenerator means for generating a reference PN code; convolver means forcorrelating a received PN code contained in a received signal with saidreference PN code to generate a correlation spike; correlation pulsegenerator means for generating a series of correlation pulsescorresponding to the polarity of said correlation spike from saidconvolver means; means for generating an early sampling pulse prior toand a later sampling pulse after a point in time at which a correlationpulse should be generated by said pulse generator means when thereceived PN code has a predetermined relationship with respect to saidreference PN code; detecting means supplied with said series ofcorrelation pulses and responsive to said sampling pulses for detectinga time deviation from said point in time of a correlation pulsegenerated by said pulse generating means; and phase control meansresponsive to detection of said time deviated correlation pulse forgenerating a phase control signal to control the phase of said referencePN code.
 6. The spread spectrum communication receiver according toclaim 5, wherein said means for detecting a time deviated correlationpulse includes a counter for counting the number of correlation pulsessampled in response to a plurality of said early sampling pulses as aresult of a time deviation representing a time advance and for countingthe number of correlation pulses sampled in response to a plurality ofsaid later sampling pulses as a result of a time deviation representinga time delay, said counter generating a deviation signal indicative ofthe amount of advance or delay time deviation based on its count valueand supplying said deviation signal to said phase control means, saidphase control means generating said phase control signal in response tosaid deviation signal.
 7. The spread spectrum communication receiveraccording to claim 5, wherein said code generator means is responsive tosaid phase control signal for controlling the phase of said reference PNcode.
 8. A spread spectrum communication receiver, comprising:referencePN code generator means for generating a reference PN code; convolvermeans for correlating a received PN code contained in a received signalwith said reference PN code to produce a correlation spike; correlationpulse generator means for generating a series of correlation pulsescorresponding to the polarity of said correlation spike from saidconvolver means; means for generating an early sampling pulse prior toand a later sampling pulse after a point in time at which a correlationpulse should be generated by said pulse generator means when thereceived PN code has a predetermined relationship with respect to saidreference PN code; window pulse means for generating a window pulsebased on said sampling pulses and having a predetermined time width; anddata demodulating means responsive to said window pulse for extracting acorrelation pulse from said series of correlation pulses anddemodulating data therefrom.
 9. The spread spectrum communicationreceiver according to claim 8, wherein said window pulse begins whensaid early sampling pulse begins and terminates when said later samplingpulse terminates.
 10. The spread spectrum communication receiveraccording to claim 8, including matching means for detecting a relativematch between said demodulated data and a predetermined pattern in orderto detect the start timing of information data present in saiddemodulated data and to produce a detection output for an exteriorcircuit, said matching means being weighted according to saidpredetermined pattern.
 11. A spread spectrum communication receivercomprising:reference PN code generator means for generating a referencePN code; convolver means for correlating a received PN code contained ina received signal with said reference PN code to produce a correlationspike; correlation pulse generator means for generating a series ofcorrelation pulses corresponding to the polarity of said correlationspike from said convolver means and having a pattern; first detectingmeans for detecting coincidence between the pattern of said series ofcorrelation pulses and a pattern whose bits are all "1" or "0" and forproducing a detection output in response to detection of saidcoincidence; initial synchronizing means responsive to said detectionoutput for controlling the phase of said reference PN code to establishinitial synchronization between said received and reference PN codes;data demodulating means for extracting a desired pulse from said seriesof correlation pulses and for demodulating data therefrom; and seconddetecting means for detecting coincidence between said demodulated dataand one of a predetermined Barker code and its phase-inverted patternand for producing a detecting signal representing the start timing ofinformation data contained in said demodulated data.